Manifolds rust or corrode with time and sooner or later they will spring a leak and fill
your engines cylinders and/or oil pan with water.

Try to flush your engine with hose water after each and every use to help your exhaust to last.

REPLACE your exhaust elbow gaskets every year or sooner if you suspect a leak.
The wet exhaust elbow gaskets are prone to leakage. The metal surfaces to which the gaskets seal get rusted or
corroded and when this happens the gaskets fail and allow water into the engine. Always use the correct factory gaskets.
The gasket sealing surfaces MUST be perfect. They must be flat and shiney metal in appearance. If the metal looks brown try
to sand or mill the surfaces down until shiney metalic and perfectly flat.

Freezing with water left in the manifolds will crack your manifolds.
Make sure you drain all the water out of your exhaust when winterizing your engine.

Safety
Boats can explode. Moving parts can rip your off your fingers.
Hot exhaust can burn you to the bone and props can slice you up.
One spark near a battery can cause an explosion.
You can never be too careful. Remove the battery from the boat before
working with fuel. Always disconnect the batteries negative terminal first.
Clean up any spilt fuel and let ALL of the fumes dissipate before installing
the battery and starting the motor. Pulleys and Belts can grab your clothes and hair.
Don't wear loose clothing and keep your hair up under a hat.
Always wear safety glasses.
Be smart.